Non-actinic fluorescent lamp



Dec. 16, 1958 L. BURNS NON-ACTINIC FLUORESCENT LAMP Filed De c. 2. 1955ANGSTRQM UNITS 3025 N30 3340 IN VEN TOR! NON-ACTINIC FLUORESCENT LAMPLaurence Burns, Swampscott, Mass, assignor to Sylvania Electric ProductsInc, Salem, Mass, a corporation of Massachusetts Application December 2,1955, Serial No. 551,280

3 Claims. (Cl. 313-109) This invention relates to electric dischargelamps and particularly to fluorescent lamps.

An object of the invention is to reduce eye fatigue and the like fromfluorescent lamps by eliminating or reducing the amount of ultra-violetlight emitted by such lamps. A feature of the invention is a fluorescentlamp envelope which transmits visible but absorbs ultra-violet light andanother feature is a coating for this same purpose. Other objects,advantages and features of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingin which:

Figure l is a representation of a spectrogram of an ordinary fluorescentlamp;

Figure 2 is a lamp according to the invention;

Figure 3 is a fixture according to the invention;

Figure 4 is another fixture according to the invention;

Figure 5 is a broken view in section, of a lamp according to amodification of the invention; and

Figure 6 is a broken view, in section, of a lamp according to furthermodification of the invention.

It has been found that fluorescent lamps often produce eye fatiguegreater than that from incandescent lamps. This may be due to variousfactors, one of which is the ultra-violet emission from the lamps. Thelamps ordinarily produce the mercury spectrum, which includes radiation,or lines as in Figure 1, at roughly 3650 Angstrom units, and also at3340, 3130 and 3025. These radiations cause the eye itself to fluoresce,and by thus reducing the sharpness of vision under the light, cause eyestrain. When the fluorescent materials used are a blend of magnesiumtungstate and zinc manganese beryllium silicate, there is very littleultra-violet radiation from the fluorescent powders themselves, but themercury radiations previously mentioned still are present. When calciumtungstate is used as one of the fluorescent materials, radiations justbelow the blue are produced and when calcium silicate, activatedconjointly with manganese and lead is used, considerable radiation ofabout 3200 Angstrom units is produced. The latter phosphor produces abull visible light but also some ultraviolet; it has two separatedemission bands.

Figure 2 shows a glass envelope 1, containing an inert gas, for example,argon at a few millimeters pressure, and mercury vapor, and having anelectrode 2, 3 sealed into each end by the lead-in wires 4, 5, 6, 7. Afluorescent coating 3 is on the inside of the envelope 1. The envelope 1has heretofore been made of lead or lime nited States Patent .ZfifiifibbPatented Dec. 16, 1958 ice - to radiations below 3000 Angstrom, such asthe 2537 glass which transmits ultraviolet in the region above 3000Angstrom mercury radiation. Such a material would be Z1110 vanadate oruranium-activated calcium fluoride or sodium fluoride, for example.These give a yellow or yellowish-green light, and the main fluorescentmaterials used would have to be such, or so blended, as to give a whitelight, or the desired color, in the presence of this additional light.

In some cases it may be more convenient to us an ultraviolet absorbingglass or plastic in the fixture, as shown schematically in cross-sectionin Figure 3, where the lamp 10 is surrounded by the reflector 11 and thelight transmitting, ultra-violet absorbing piece 12.

In other cases, it may be desirable to use the louvres. 13 as shown inFigure 4. These will shield the eyes from the direct light from the lampor lamps 10 in the reflector 11, and may have a coating 18 of asubstance which reflects'visible light but absorbs ultra-violet. Thefluorescent materials previously mentioned may be used for this purpose,eing applied in a varnish, a lacquer, or a plastic. The louvres 13 maybe, for example, as shown in application, Serial No. 481,040, filedMarch 29, 1943, by Rene G. Maurette. When a blend of fluorescent powdersincluding calcium silicate activated with both manganese and leadconjointly is used, it may be desirable to mix in with the blend a greenor yellowishgreen fluorescing material, responsive to the ultravioletemitted by the calcium silicate. This will eliminate or reduce theamount of ultra-violet emitted by the coating-as well as that emitted bythe mercury vaporand will at the same time add some green light to thatemitted by the calcium silicate. Since the spectrum of calcium silicate,even when supplemented by the spectrum of magnesium tungstate physicallyadmixed with it, is generally slightly deficient in the green, thisserves a double purpose.

The uranium-activated calcium fluorides and other materials of U. S.Patent 2,323,284, issued June 29, 1943 to W. P. Toorks may prove usefulin this respect. Zinc Vanadate may be useful if the yellow portion ofthe spectrum is to be enhanced.

The usual lead or lime glass used in fluorescent lamp bulbs decreasesrapidly in transmission with wavelength, as the latter is reduced below3300 Angstroms, so that the wavelengths above this value are the chiefones to be absorbed from the present lamps although some of the lowerwavelengths down to 3000 Angstroms are trans mitted to a lesser extent.When the fluorescent material used has high emission below 3300Angstroms, considerable radiation below that wavelength may be emitteddespite the low glass transmission of regular bulbs at that wavelength.

Where an absorbing layer 14, 15 is used in the lamp, it should beordinarily placed between the regular layer 8 and the glass envelope 1,unless it is placed on the outside of the glass envelope, or unless ithas high transmission for the 2500 Angstrom radiation which excites themain fluorescent material. In addition to the absorbing materialspreviously mentioned, zinc or titanium oxides will be found quiteeffective, zinc being especially effective against the 3650 Angstromwavelengths and lower. Zinc oxide will also be found good as a materialfor the coating 17, 18 on reflector 11 and louvres 13, in

Where the glass transmission is reduced by addition I of ferrous oxideto the batch from which it is made, 0.2 to 1% will generally be foundsufiicient. Titanium and cerium oxides have also been found effectivefor this purpose. 1

In Figures 3 and 4, the filter 12 and louvres 13 are shown incross-section. They extend longitudinally with the tube 10.

A thin gold film on the .glass envelope may sometimes be desirable asthe filter 14, 15 which transmits visible and absorbs ultra-violetlight. Such a film has the additional advantage that it allows startingof the lamp at lower voltage and makes its starting independent of theambient humidity. In ordinary commercial fluorescent lamps as now sold,the necessary starting voltage'rises with humidity.

This rise may also be reduced in a different manner without the goldcoating, 'by providing spring metal pieces 16 electrically connected toand extending from the metal reflector 11 ordinarily used with the lamp10, and bearing on the glass envelope 1 of the lamp 111 near the cathode3. One may be used at each end of the lamp, but if the reflector 11 is,directly or indirectly, grounded to one end of the lamp, the springpiece bearing on -the glass may be used at only the ungrounded end ofthe lamp 10. The spring piece 16 will ordinarily bear-on the side of thelamp 10 nearest the reflector 11, to be out of sight and to facilitateinsertion of the lamps in its sockets. This spring piece 1'6 may, ofcourse, be used with the present commercial fluorescent lamps, which donot have ultra-violet absorbing means. And conversely, such a springpiece 16 is not at all necessary with my ultra-violet absorbing lampsunless a better starting condition is desired than is usual in presentcommercial lamps.

This application is in part a continuation of my copending applicationsSerial No. 568,737, filed December 18, 1954, now U. S. Patent No.2,799,809, Serial No. 50,608 filed September 22, 1948, now abandoned andSerial No. 206,440, filed January 17, 1951, now U. S. Patent No.2,714,903.

What I claim is:

l. A fluorescent lighting fixture comprising a metallic reflector, afluorescent lamp having a tubular envelope of light-transmitting-glassand a fluorescent coating on the inner surface of said envelope, meansfor holding said lamp in light-reflecting relationship to said reflectorand a metal piece electrically and mechanically connected to saidreflector and bearing on the outside surface of the tubular envelope ofsaid lamp.

2. The fixture of claim -1, in which the metal piece bears on saidenvelope near a cathode, to facilitate starting.

3. The fixture of claim 1, in which there is a coating of titanium oxidebetween the fluorescent coating and the inner surface of said envelope.

References Cited in the file of this patent UNITED STATES PATENTS2,112,718 Somers Mar. 29, 1938 2,135,691 Alterthum et al Nov. 8, 19382,156,068 Ruttenauer et al Apr. 25, 1939 2,264,092 McCauley Nov. 25,1941 2,774,903 Burns Dec. 18, 1956

